Methanol is available from carbon-containing sources of non-petroleum origin, such as coal for the synthetic gas route and vegetable matter by cellulose conversion. Thus, this alcohol is bound to become an essential chemical basic material for the manufacture of important synthetic intermediates. The production of light olefinic hydrocarbons from methanol is hence an attractive direction of research.
The reaction of the conversion of methanol into hydrocarbons has been the subject of numerous studies. The catalysts applied belong mostly to the class of zeolites. These crystalline silicoaluminates are particularly suitable for this type of reaction by reason of thier acid character and their fully determined structure of which the diameters of the intercrystalline channels are of the same order of magnitude as those of the majority of organic molecules.
However, one of the essential drawbacks of these methods for the catalytic processing of methanol on crystalline zeolite is constituted by the rapid deactivation of the catalyst by deposits of carbonaceous origin, which prevents any industrial development under normal economic conditions.
A modified zeolitic catalyst has been sought enabling the production essentially of unsaturated hydrocarbons having for the most part 2 to 5 carbon atoms, and whose catalytic life span is notably increased.
It is known that mordenite is one of the zeolitic silicates richest in silica. The method described in French Pat. No. 1,411,753 enables synthesis of sodium mordenite with small pores of 4 to 5 .ANG., of which the formula of the elementary unit is Na.sub.7 Al.sub.7 Si.sub.40 O.sub.94, 24H.sub.2 O. The Si/Al (atomic) ratio is close to 6 for the sodium form.
Previously, particularly according to the teaching of French Pat. No. 2,019,913, it was known that mordenites subjected to alternating multiple cycles starting by processing with steam and then refluxing by an acid, have been proposed as catalytic compositions for the conversion of hydrocarbons.
Acid mordenite, obtained by heat treatment, in air at 650.degree. C. in the ammonium form, is very active in the conversion of methanol into hydrocarbons but its life span is very short. After less than 30 minutes of reaction, it has been observed that the conversion ratio of the methanol, initially 100, becomes less than 1%.